The invention relates to the general field of magnetic disks with particular reference to GMR read heads and ways to ensure lateral stabilization.
The read element in a magnetic disk system is a thin slice of material, located between two magnetic shields, whose electrical resistivity changes on exposure to a magnetic field. Magneto-resistance can be significantly increased by means of a structure known as a spin valve (SV). The resulting increase (known as Giant magneto-resistance or GMR) derives from the fact that electrons in a magnetized solid are subject to significantly less scattering by the lattice when their own magnetization vectors (due to spin) are parallel (as opposed to anti-parallel) to the direction of magnetization of the solid as a whole.
The key elements of a spin valve structure are two magnetic layers separated by a non-magnetic layer. The thickness of the non-magnetic layer is chosen so that the magnetic layers are sufficiently far apart for exchange effects to be negligible but are close enough to be within the mean free path of conduction electrons in the material. If the two magnetic layers are magnetized in opposite directions and a current is passed through them along the direction of magnetization, half the electrons in each layer will be subject to increased scattering while half will be unaffected (to a first approximation) Furthermore, only the unaffected electrons will have mean free paths long enough for them to have a high probability of crossing the non magnetic layer. Once these electrons have crossed the non-magnetic layer, they are immediately subject to increased scattering, thereby becoming unlikely to return to their original side, the overall result being a significant increase in the resistance of the entire structure.
In order to make use of the GMR effect, the direction of magnetization of one the layers must be permanently fixed, or pinned. The other layer, by contrast, is a xe2x80x9cfree layerxe2x80x9d whose direction of magnetization can be readily changed by an external field (such as that associated with a bit at the surface of a magnetic disk). Structures in which the pinned layer is at the top are referred to as top spin valves. Similarly, in a bottom spin valve structure the pinned layer is at the bottom.
Although not directly connected to the GMR effect, an important feature of spin valve structures is a pair of longitudinal bias stripes that are permanently magnetized in a direction parallel to the long dimension of the device. In the prior art, longitudinal bias layers have been implemented as permanent magnets by using a hard magnetic material. However, this approach results in a xe2x80x9cdead zonexe2x80x9d over which the sensitivity is very low and reduces the overall reader sensitivity. The impact of the xe2x80x9cdead zonexe2x80x9d becomes more severe at high track density.
An alternative to the commonly used abutted junction stabilization scheme is the xe2x80x9cboundary exchangexe2x80x9d (BE) biased stabilization scheme. In this scheme, an antiferromagnetic film is placed on the top of the free layer at each side to replace abutted permanent magnets in the conventional abutted junction heads. The magnetization at the side region of the free layer is pinned by the interfacial antiferromagnetic exchange coupling field. The sensor region at the center of the free layer, on the other hand, is free of any pinning field. This design eliminates the xe2x80x9cdead zonexe2x80x9d problem and therefore significantly increases the reader sensitivity.
In order to obtain sufficient antiferromagnetic exchange coupling with the free layer, the interface between the free layer and the AFM layer needs to be fresh and clean. The prior art has dealt with this problem by partially etching away the free layer at the side region and then refilling with free layer material, following up by the deposition of the AFM film layer. However, this approach is becoming progressively more difficulty as the free layer grows thinner, due to difficulties in etch control and surface cleaning.
FIG. 1 is a schematic view of a prior art xe2x80x9cboundary exchangexe2x80x9d bias stabilization head. The figure shows a bottom spin valve of the prior art in which the longitudinal bias is of this type. Seen there is substrate 11 which supports pinned layer 12. Layer 13 is the non-magnetic spacer layer and layer 14 is the free layer. Antiferromagnetic stripes 15 provide the longitudinal bias while layer 16 represents the conductive leads. The problems associated with this approach are increased processing difficulties with the free layer where it is partially removed before depositing the top AFM.
A routine search of the prior art was performed with the following references of interest being found:
In U.S. Pat. No. 5,325,253, Chen et al. show a stabilized MR transducer using a canted exchange bias. An antiferromagnetic layer directly contacts the side region of the free layer to bias the magnetization in the side region of the free layer in the desired direction, in a similar manner to that illustrated in FIG. 1. There is no GMR capping layer no layer between the free layer and the biasing layer, the antiferromagnetic layer being in direct contact with the free layer. Canting is used in U.S. Pat. No. 5,325,253 to align the magnetization at the side region of the free layer to be parallel to that in the center active region of the free layer, therefore eliminating the free charges due to magnetic moment mismatch between the side region and the center region and improving stability.
Kung et al. (U.S. Pat. No. 5,680,281) show an edge (horizontal)-biased MR sensor. U.S. Pat. No. 5,958,611 (Ohta et al.), U.S. Pat. No. 5,856,897 (Mauri et al.), U.S. Pat. No. 5,859,754 (Tong et al.), U.S. Pat. No. 6,230,390 (Guo et al.), and U.S. Pat. No. 5,995,338 (Watanabe et al.) are related patents.
It has been an object of at least one embodiment of the present invention to provide a horizontal stabilization scheme for a spin valve structure.
Another object of at least one embodiment of the present invention has been that said structure not suffer instability problems arising from multiple domain states.
Yet another object of at least one embodiment of the present invention has been that said structure should keep the free layer from being attacked during wafer fabrication.
Still another object of at least one embodiment of the present invention has been that said structure provide improved side reading suppression.
A further object of at least one embodiment of the present invention has been to provide a process for manufacturing said structure.
These objects have been achieved by introducing two important changes into prior art designs for longitudinal biasing schemes. Instead of biasing by means of a permanent magnet or through exchange coupling with an antiferromagnetic layer the magnetostatic field emanating from a nearby, but not contiguous, layer is used. Further, to obtain optimum stability with this scheme the bias, instead of running parallel to the easy axis of the free layer, is canted away from it towards the direction of the demagnetizing field of the pinned layer. This canted bias field is applied to the free layer through magnetostatic coupling which does not require direct contact between the bias and free layers. This approach simplifies the manufacture of the structure since close control of etching (to remove part of the free layer) is no longer needed and a capping layer may be laid down over the free layer immediately following its deposition, thereby protecting it from contamination.